Process for the reductive dimerization of alpha,beta-olefinicallyunsaturated nitriles or esters



3,489,789 PROCESS FOR THE REDUCTIVE DIMERIZA- TION F 01,;8-OLEFINICALLY UNSATURATED NITRILES 0R ESTERS Robert Alfred Dewar, Volker Elmar Maier, and Margaret Anthea Riddolls, Melbourne, Victoria, Australia, assignors to Imperial Chemical Industries of Australia and New Zealand Limited, Melbourne, Victoria, Australia, a company of Australia No Drawing. Filed Apr. 7, 1965, Ser. No. 446,430 Claims priority, application Australia, Apr. 16, 1964, 43,311/64; Aug. 27, 1964, 48,630/64 Int. Cl. C07c 69/44, 121/20, 121/26' US. Cl. 260-4653 16 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a process for the manufacture of dicarboxylates, dinitriles and dicarboxamides in particular it relates to the manufacture of dinitriles and especially to the manufacture of adiponitrile from acrylonitrile. The hydrodimerisation of acrylonitrile to adiponitrile according to the schematic equation has been disclosed by Knunyants and Vyazankin (Bull. Acad. Science U.S.S.R., 1957, pp. 238-240 who used as the reducing agent an amalgam of mercury and an alkali metal and strong hydrochloric acid as the medium containing the acrylonitrile in dilute solution. With this system adiponitrile was formed, but a considerable part of the acrylonitrile was converted to propionitrile and this has made the process uneconomic.

It is also known that the formation of propionitrile can be depressed if a process of actual electrochemical reduction is employed which is characterised in that an electric current is passed from a separate anode through a solution of acrylonitrile in contact with a cathode having a hydrogen overvoltage greater than copper under specified conditions of hydrogen ion concentration and at concentrations of acrylonitrile in excess of 10%. It is advantageous to use in the specified direct electrolytic process, certain aliphatic and heterocyclic amine salts, quaternary ammonium salts and other salts. This is in clear contradistinction to the indirect methods as preparing sodium amalgam by electrochemical reduction of sodium salts followed by mere contacting of a solution of the olefin with the sodium amalgam.

We have now found that the hydrodimerisation of acrylonitrile by alkali metal amalgams with high yield of adiponitrile, depression of the formation of ropionitrile and high conversion is possible in the absence of an external electrolytic circuit when certain organic cations are added to the reaction medium.

Accordingly we provide a process of reductive dimerisation of olefinic compounds selected from the group consisting of a,,8-olefinic nitriles, esters of aliphatic a s-ole- United States Patent O ice finic carboxylic acids and OL,B-01efil'liC carboxamides, in the absence of an external electrical circuit wherein the pable of providing reactive hydrogen by reacting a metal amalgam selected from the group consisting of alkali and alkaline earth metal amalgams with said medium in the presence of at least one salt capable of forming alkylated cations in said medium.

The invention is especially useful for acrylonitrile and alkyl substituted acrylonitriles (as hereinafter defined).

Preferably the olefinic compounds are monoolefins.

By the term salts capable of forming alkylated cations in aqueous media we mean salts forming e.g. ammonium, phosphonium or sulphonium cations such as tetraalkylammonium salts, tetraalkyl-phosphonium salts, trialkylsulphonium salts. One of the benefits of the addition of these salts is the depression of the undesired full hydrogenation of the double bond.

Particularly effective are the quaternary ammonium salts. Accordingly we also provide a process as described characterised by the presence of a quaternary ammonium salt. The nature of the substituents on the oninm cation aifects the efficacy of our process in regard to the degree of suppression of the undesired full hydrogenation reaction such as the undesired formation of propionitrile from acrylonitrile. Thus e.g. we have found that certain pyridinium salts are considerably less effective in this respect than tetraethylammonium salts or saturated heterocyclic quaternary compounds such as piperidinium or piperazinium salts.

Accordingly we provide a preferred process characterised further by the presence of a quarternary ammonium salt excluding, however, salts in which the quaternary nitrogen is part of a ring structure of aromatic character.

The excluded, less effective salts are identifiable by the development of intense colours in the presence of the amalgam, which colours fade or change on exposure to air.

We believe without prejudice to the invention that the selection of particularly effective quaternary ammonium compounds is to be based on the geometry of the quaternary ammonium ions, which we consider must be such that they are geometrically capable of so packing themselves together on the reducing surface that the access of undesired molecules or ions e.g. of either acrylonitrile or of water or of hydrated hydrogen ionswhichever causes full hydrogenationto the reducing surface is prevented or minimised. Thus the highly elfective tetraethylammonium and cetyltrimethylammonium ions can be shown by means of molecular models to be capable of close packing on a surface, while tetra n-butyl and methyl tri-n-butylammonium ions which we found to be less effective appear to leave spaces between adjacent ions large enough for the access of hydrated hydrogen ions to the surface because of the three or more long butyl chains. We consider that the more effective cations are to be found among the tetraalkylammonium compounds bearing at least two short alkyl radicals, which may be the same or different, where the short alkyl radical is selected from the group consisting of methyl, ethyl, propyl, isopropyl and isobutyl.

Accordingly we provide a process characterised further in that the reaction is carried out in the presence of a quaternary tetraalkylammonium salt in which salt at least two alkyl radicals which may be the same or different are selected from the group consisting of methyl, ethyl, propyl, isopropyl and isobutyl and the remaining two alkyl radicals which may be the same or different may be short or long and wherein, optionally, any two or three of said alkyl radicals may be linked directly or, optionally, through at least one further nitrogen or at least one oxygen or sulphur atom to form a non-aromatic monocyclic or bicyclic ring system. Said remaining two alkyl radicals may have one to twenty-four or more carbon atoms where the upper limit of chain length is given by the requirement that the resulting compound must remain appreciably soluble in the aqueous medium.

As well as alkyl we may include alkenyl and alkynyl, particularly alkenyl radicals having one double bond in positions other than vicinal to the quaternary nitrogen. However, no special benefit is derived from unsaturation and alkyl is therefore preferred.

While the quaternary ammonium salts defined above substantially improve the ratio of adiponitrile to propionitrile formed over that obtained in the absence of a quaternary ammonium salt as defined, it remains a desirable target to reduce the formation of propionitrile to a level so low that in technical practice it can be discarded, i.e. does not require recovering or recycling or can even be disregarded as an impurity in the final product. Hence conversions to propionitrile less than 20% and approaching 1% are particularly desirable. We have found that particularly low propionitrile conversions are obtained in the presence of quaternary ammonium compounds having certain proportions of short, medium and long chain alkyl substituents.

Accordingly a particularly preferred process comprises the reductive dimerisation of acrylonitrile, alkyl substituted acrylonitriles and (1, 8 olefinic acid esters and carboxamides as defined above respectively wherein in a medium capable of providing hydrogen and preferably maintained at neutral to alkaline conditions the reduction is carried out by reacting an alkali metal amalgam or an alkaline earth metal amalgam with said medium in the presence of a quaternary ammonium compound of the formula RIRIIRIIIRIVNX wherein R and R which may be the same or difierent, are selected from the group consisting of methyl, ethyl, isopropyl, n-propyl and isobutyl, R is alkyl including cycloalkyl, R is alkyl and X is an anion and wherein, optionally, any two alkyl radicals selected from the group consisting of R R and R may be linked directly or, optionally, through at least one further hetero atom selected from the group consisting of nitrogen, oxygen and sulphur to form a non-aromatic ring and wherein furthermore, optically, a third alkyl radical selected from the group consisting of R R and R may be linked to said first ring directly or through at least one further hetero atom selected from the group consisting of nitrogen, oxygen and sulphur to form a non-aromatic 'bicyclic ring system.

As well as alkyl we may include here again alkenyl and alkynyl, particularly alkenyl radicals having one double bond in positions other than vicinal to the quaternary nitrogen. However, no special benefit is derived from unsaturation and alkyl is therefore preferred.

The alkyl radicals R and/or R which may be the same or different, may be short or long, say C to C and more where the upper limit, again, is given by the requirement that the compound must remain appreciably soluble in the reaction medium.

The alkyl group may be branched and may furthermore carry certain non-alkyl substituents in the carbon chain. However, aromatic substituents must not be in the alpha position to the quaternary nitrogen; thus benzyl is unsuitable as R or R but (u-methyl-B-phenyDethyl is acceptable. Yet, in general no further improvement is achieved by substitution in R or R and among the substituents the less polar groups, closer in character to the straight chain alkyl group, are better than polar groups. Thus acetyl choline is more effective than choline itself.

Solubility either in water or in acrylonitrile of thesalt capable of forming alkylated cations is desirable and high solubility is preferred; with higher amounts of Water an on of inorg nic acids g. ch o ide or b omide a satisfactory. When very low amounts of water are used the organic anions, e.g. p-toluene sulphonate, which are more soluble in acrylonitrile, are more convenient.

A particularly suitable salt is tetraethylammonium ptoluene sulphonate. Other preferred salts are trirnethylcetylamrnonium bromide, tetramethylammoniurn ptoluene sulphonate and trimethyl(ethyl)ammonium bromide.

The operative amount of the salt capable of forming alkylated cations in the reaction medium varies over wide ranges. While the benefit of the invention i.e. the depression of the formation of the nitriles and esters of the undesired fully hydrogenated alkanoic acids is appreciable at concentrations as low as 0.5 part and as high as 50 parts by weight of alkylated cationic salt per parts of acrylonitrile, concentrations between 10 and 30 parts of alkylated cationic salt per 100 parts of reaction mixture are most effective and are therefore preferred.

Optionally certain inorganic salts may be added to the reaction mixture as promoters. Suitable promoters are e.g. chromium compounds such as chromic chloride or sodium chromate.

The amount of promoter used may vary over a wide range e.g. between 1 to 50 parts per million parts of reaction mixture. However, We have established in separate experiments, e.g. Experiment No. 23, by careful removal of all analytically measurable quantities of the promoters, that the presence of promoters is not essential for the successful operation of our process.

The medium capable of forming hydrogen with an alkali metal amalgam is preferably water; however, the use of those lower alcohols which themselves do not react with acrylonitrile to form undesired by-products and/or mixtures of water and alcohols is within the scope of the invention. The use of further polar inert solvents added e.g. so as to increase the solubility of the cation-yielding salts and/or the monomer is within our invention. Suitable solvents are e.g. dioxane, acetone, dimethylforrnamide or ethylene glycol. The amount of Water, again, may vary over Wide ranges: relatively small amounts of water e.g. as little as 1 mole per 10 moles of acrylonitrile are operative and in general high acrylonitrile concentrations are conducive to good yields; even less than 1 mole of water may be used but control then becomes more difiicult since water may be exhausted in the reaction too rapidly and a yellow by-product may be formed. Increased water concentrations facilitate removal of the byproduct salt formed by neutralisation of the alkali metal and it is therefore convenient to use considerably more water, say 3 to 20 moles of water per mole of acrylonitrile. Thus when cetyltrimethylammonium bromide was used as the cationic salt, a ratio of about 3.8 moles of water per mole of acrylonitrile, rising during the reaction to a ratio of about 12.5 moles of water per mole of acrylonitrile, was found to be both eifective and convenient for removal of the by-product. We have found furthermore that, at low water concentrations, higher molecular weight products, presumably hydro-trimers and hydro-tetramers of acrylonitrile, may be formed. These undesired by-prodnets are depressed as the water content of the reaction medium increases, particularly at concentrations of 20 or more moles of water per mole of acrylonitrile. Thus higher water contents, e.g. 39 moles of water per mole of acrylonitrile rising during the reaction to a ratio of at least 72:1 moles, were demonstrated to be operative and to depress the formation of the undesired high molecular weight by-products.

When the higher water concentrations are used the aqueous phase may separate from the organic acrylonitrile/adiponitrile phase; this does not prevent the reaction from proceeding and it further facilitates separation of the inorganic neutralisation product e.g. sodium bicarbonate from the reaction mixture as well as temperature control because the water excess assists in absorbing ny un esire sud nly evolved he t of reac ion. In gen eral the amount of water is not narrowly critical for the operation of the process.

The benefits of our invention, in particular the depression of the reaction leading to propionitrile by use of organic cations as described, are most pronounced under neutral to alkaline conditions. By neutral to alkaline we mean a pH not substantially less than 7 and not more alkaline than the pH at which cyanoethylation occurs, i.e. below about 9.5. We have, however, found that a lesser but still substantial depression of the reaction leading to propionitrile may be also attained in acid medium. Thus we have found that the addition of cetyltrimethylammonium bromide reduces the formation of propionitrile even at a pH of 1 to a slight extent, while at a pH of 1.5 the ratio of adiponitrile to propionitrile was increased substantially over that obtained in the absence of the quaternary agent and increased progressively further with the pH until it reached its optimum value between the pH values 7 and 9.5. Accordingly we provide a process as defined above operative in the range from a pH of 1.5 to 9.5, the preferred range being 7 to 9.5. Since in conducting the hydrodimerisation reaction with alkali metal amalgams the hydroxide of the alkali metal is progressively produced, it is necessary to maintain an addition of acid. This can be done by the constant addition of a strong acid, but maintenance of the acid-base balance, especially when low water concentrations are used, then may require particularly careful control possibly even the use of automatic instrumentation. Alternatively a weak acid may be used, the alkali or alkaline earth salt of which is not so basic as to lead to the undesired pH above 9.5. For economic reasons inorganic weak acids are preferred. A well-known convenient method of pro ducing a weak acid is the addition of a strong acid to a buffer, e.g. the addition of phosphoric acid to a sodium dihydrogen-phosphate/disodium-hydrogen phosphate buffer system.

A convenient and preferred method of controlling the pH between 7 and 9.5 is the addition of carbon dioxide by maintaining in the reaction vessel a suitable concentration of the gas and promoting the rate of solution of the gas in the reaction liquid e.g. by agitation of the liquid. An atmosphere of pure carbon dioxide is preferred because it avoids the complications resulting from recovery of gaseous acrylonitrile from a large inert gas stream. Slightly superatmospheric pressure is convenient, but higher and even reduced pressures may be used. By reaction of the alkali hydroxide with the carbon dioxide in the presence of water in the reaction medium, the bicarbonate of the alkali metal is formed and precipitated. Conveniently it may be separated e.g. by intermittent filtration or by continuous filtration e.g. by circulating part of the reaction mixture through a filter, so as to avoid the contamination of the reaction mixture with large amounts of the neutralisation product.

Instead of alkali metal amalgams it is possible to use the amalgams of the alkaline earths. In normal commercial practice, however, sodium or potassium amalgams are preferred since these are readily available from large scale processes and the corresponding neutrallsation byproducts are of commercial value.

The content of alkali or alkaline earth metal in the amalgam may also vary over wide ranges from saturation point to minute concentrations; since under our process conditions the amalgam decomposes rapidly the actual concentration in operation is not easily assayed. Depending on reaction conditions lower concentrations, e.g. below 0.1% of sodium in mercury, are convenient when excessive evolution of heat is to be avoided.

Ambient temperatures between 10 and 35 C. are suitable for the reaction and are preferred, but both lower and higher temperatures may be used. Thus, although above 35 C. the propionitrile content increases gradually, temperatures above 35 C. may be desirable so as to reduce the formation of higher molecular weight hydrooligomers as well as for chemical engineering reasons; since an appreciable temperature differential between reactants and cooling water is necessary for heat transfer, operation above 35 C. may be desirable to avoid the need to use refrigeration for cooling. The temperature range preferred on technical scale is therefore wider, between the freezing point of the aqueous medium and 60 C.

Since the formation of polymer is undesired we furthermore prefer in the practice of our invention to add a suitable inhibitor of the vinyl-type polymerisation. Suitable inhibitors are the polymerisation inhibitors known from the technology of polymerisation of vinyl monomers. A particularly suitable, preferred inhibitor is N,N-dimethyl p-nitrosoaniline. Thus a few parts of N,N-dimethyl p nitrosoaniline per million parts of monomer are effective in suppressing the formation of polymer.

Our process may be carried out batchwise or continuously. In the batch process the reactor may e.g. consist of a closed vessel, preferably provided with a relatively fiat bottom, permitting the formation of a large surface area for the amalgam; an inlet or inlets for the liquid reactants and water together with promoter, if used, cationic salt and polymerisation inhibitor; an inlet for the acidifying substance which, when carbon dioxide is used, conveniently may be a dip tube with a porous gas distributor immersed in the water-monomer phase; a cooling coil or jacket in contact with the aqueous and/ or amalgam phase; a stirrer which may be adjusted to agitate the aqueous phase and/or amalgam phase or a separate stirrer for either phase; an outlet for the reactants and, preferably, a separate outlet for the aqueous phase and for removal of the precipitated neutralisation product e.g. sodium bicarbonate.

In steady state operation the reactants are fed continuously, in the proportions of the desired steady state reaction; a proportion of the acrylonitrile/water phase, containing the precipitated salt is removed continuously, the salt is separated e.g. by centrifuging and the filtrate is recycled to the reactor. Another portion or alternatively a fraction of said filtrate, is discharged and worked up to yield the desired hydrodimer and the unconsumed raw materials. According to one method of steady state reaction the two phases may flow lengthwise horizontally through the reactor, which may be a pipe or trough, from inlet to outlet is avoided; consequently there is a falling concentration gradient of alkali metal in the amalgam and a rising concentration gradient of acrylonitrile dimer from the entry to the outlet of the reactor. Techniques of continuous operation with the phases travelling through the reactor cocurrently or counter-currently are known in the art.

. In both batchwise and continuous operation the product is worked up by separation of the liquid phases e.g. by decantation, removal of solid salt as described, fractional distillation or solvent extraction of the aqueous monomer/hydrodimer/cationic salt phase in a manner known per se and the unreacted raw material is recovered.

By the term alkyl substituted acrylonitriles throughout this specification, we mean acrylonitrile hearing at least one alkyl substituent having up to 4 carbon atoms in the a or {3 carbon atoms joined by the double bond. As wellas alkyl we may wish to include alkenyl and alkynyl where the unsaturated bond is not adjacent to the 11,,8 double bond of the acrylonitrile. However, it is already known that in respect of hydrodimerisation the 0a,}? mono-olefinic mono-or di-carboxylates are equivalent to the corresponding nitriles. Hence it is within our invention to apply the process as described in an analogous manner to the hydrodimerisation of mono-or dicarboxylates to parafiinic dior tetra-carboxylates.

One advantage of our invention is the high yield of the hydrodimer attainable, up to of the monomer used. The actual yield of the hydrodimerisation reaction itself may be even higher, as the losses in the laboratory experiment occur principally during the work-up and are likely to be reduced on technical scale.

A further advantage resides in the high conversion of acrylonitrile attainable.

Yet another advantage resides in the fact that the reaction occurs in the absence of an external electrical circuit. This is a useful result as the amalgam can be formed separately at high electrochemical efficiency and low voltage, no diaphragm is required and the anode reaction may be used for some other useful purpose such as the manufacture of chlorine, as e.g. in the large scale caustic/ chlorine manufacture in mercury cells. In addition the sodium or other alkali metal from the decomposition of the amalgam can be converted into yet another useful byproduct.

Our invention is now illustrated by, but not limited to, the following examples.

EXAMPLE 1 The reactor consisted of a closed 250 ml. Erlenmayer flask, fitted with a Quick-fit dropping funnel; a sealedin tube for the introduction of carbon dioxide and a water bath, used to keep the reaction temperature at approximately 20 C.

A solution was prepared containing 15.17 g. acrylonitrile, 6.86 g. tetraethylammonium p-toluene sulphonate, 1.07 g. water, 0.43 g. chromic chloride (CrCl -6H O) and 20 microgrammes N,N-dimethyl p-nitrosoaniline. This was added to the reactor containing 20 ml. mercury which reactor had been flushed out with carbon dioxide. A slight positive pressure of carbon dioxide was maintained in the vessel during the reaction.

60 ml. of sodium amalgam was prepared by electroylsing a 40% w./v. aqueous solution of sodium hydroxide between a platinum foil anode of cylindrical shape having a surface area of 1 in. and a mercury pool cathode of a surface area of 4 in. at a current flow of 4 amps. The amalgam was run from the cell and dried. A portion of this amalgam was found by hydrogen evolution to give 1.22 mg. of hydrogen per ml. of amalgam. 25.6 ml. of amalgam was added to the reaction vessel over a period of 20 minutes. During this time and for an extra 7 minutes after the addition the flask was shaken vigorously by hand.

The unreacted acrylonitrile was distilled from the vessel under reduced pressure. The weight of recovered acrylonitrile was 13.11 g. The reaction vessel was washed out three times with 20 ml. of water per washing, followed by five washings with 8 ml. methylene chloride per washing. The aqueous phase was extracted seven times with 8 ml. of methylene chloride each time. The combined methylene chloride washings were extracted twice with 15 mls. of water, then the methylene chloride was evaporated off over a water bath. The residue after evaporation was heated to 130 C. for 10 minutes to drive off any residue of water. The weight of the residue was 1.64 g. Gas chromatographic and infra-red analysis indicated that no propionitrile was present in the residue and the product appeared to be pure adiponitrile. Subsequent liquid chromatography showed, however, that higher molecular weight impurities, apparently dimers and trimers of acrylonitrile were also present.

The quantities obtained represent the following materials balance:

Percent Acrylonitrile feed converted to crude adiponitrile 10.5 Acrylonitrile feed converted to propionitrile Not detected Acrylonitrile feed recovered as acrylonitrile 86 Crude adiponitrile yield on acrylonitrile consumed 75 Crude adiponitrile yield on hydrogen available from amalgam 93.3 Purity of crude adiponitrile 60 Yield of pure adiponitrile on acrylonitrile consumed a"tuna.".-, 45

EXAMPLE 2 To the reactor as described in Example 1, which had been flushed out with carbon dioxide, were added two solutions; the first solution contained 4.0 g. of trimethylcetylammonium bromide, 0.43 mg. of chromic chloride (Cr.Cl 6H O) in 10.10 g. of water; the second solution contained 20 microgrammes of N,N-dimethyl p-nitrosoaniline in 8.17 g. of acrylonitrile; furthermore 20 ml. of mercury was added to the reactor.

ml. of sodium amalgam was prepared in a cell identical to that in Example 1. A current of 4.3 amperes was passed through the cell for 82 minutes. The amalgam was run from the cell, dried and stored in the dropping funnel under an atmosphere of nitrogen. A portion of this amalgam was found by hydrogen evolution to give 2.57 mg. of hydrogen per ml. of amalgam. 41.5 ml. of this amalgam was added to the reaction vessel over a period of 33 minutes. During this time and for a further 5 minutes after the addition the flask was shaken vigorously by hand. The temperature was maintained at about 20 C. by partial immersion of the flask in a bath of tap water.

The amalgam dropping funnel was removed, 20 ml, of water was added to the flask and a Dean and Starke apparatus was fitted to the flask. The flask was heated and 2.95 ml., i.e. 2.36 g. of unreacted acrylonitrile was recovered in the Dean and Starke apparatus. The contents of the flash were transferred to a separating funnel. The reaction vessel was Washed out three times with 10 ml. of methylene chloride. The aqueous phase was extracted six times with 10 ml. of methylene chloride. The combined methylene chloride was evaporated from the combined extracts and the residue obtained from this was heated to 130 C. for 10 minutes to drive 01f any residue of water. The weight of the residue was 5.65 g. 'On infrared and gas chromatographic analysis this appeared to be substantially pure adiponitrile free from propionitrile, but subsequently oligomeric impurities were detected in the crude product by liquid chromatographic analysis.

Materials balance: Percent Acrylonitrile feed converted to crude adiponitrile 67.9 Acrylonitrile feed converted to propionitrile Not detected Acrylonitrile feed recovered as acrylonitrile 28.8 Crude adiponitrile yield on acrylonitrile consumed 95.5 Crude adiponitrile yield on hydrogen available from amalgam 99 Purity of crude adiponitrile 65 Yield of pure adiponitrile on acrylonitrile consumed 62 EXAMPLES 3-20 A series of small scale experiments was carried out using apparatus of similar shape but of approximately one quarter of the capacity of Example 1. The purpose of the experiments was to establish to what extent the range of the principal experimental parameters is critical; the product as obtained was analysed by gas chromatography and the main effect, namely the relative proportion of adiponitrile to propionitrile was determined, i.e. the depression of the propionitrile formation was assayed and the formation of impurities and/or polymer was observed. The amount of oligomeric impurities formed from acrylonitrile was not determined.

Results are summarised in Table 1. In this table concentrations of the reactants are expressed as molar percent, 100% being the sum of water, acrylonitrile and the cationic salt; the concentration of acrylonitrile-not shown-is the balance to 100%. The concentration of the minor additives-promoter and polymerisation inhibiton-are expressed as parts by weight per 1 million parts of the reaction mixture comprising acrylonitrile, water and cationic salt. The relative proportions of the two principal reaction products, adiponitrile and propionitrile, are expressed as Weight percent.

Examples 3 and 4 demonstrate yields obtainable outside this invention and indicate the large amount of propionitrile formed. Examples 5, 6 and 7 demonstrate the depression of the formation of propionitrile in the presence of quite small amounts of cationic salts according to this invention.

Examples 8 to 16 demonstrates the suppression of propionitrile formation in the presence of several quaternary ammonium salts at varying concentration of quaternary salt, water, aerylonitrile, promoter and polymerisation inhibitor. Examples 8 and 9 approach the lower limit of water concentration at which exhaustion of water during the reaction with the concomitant formation of a yellow by-product can be conveniently avoided. Examples 17 to 19 demonstrate the suppression of propionitrile at somewhat lower acrylonitrile/water ratios i.e. at higher water concentrations which facilitated the removal of sodium bicarbonate. In Example 19 the reaction mixture consisted of two phases, an aqueous phase containing essentially all the sodium bicarbonate and an organic acrylonitrile/adiponitrile phase which readily of the sodium bicarbonate. Example 20 demonstrates very high water content.

was added to the flask. The flask was thoroughly purged with carbon dioxide. Sodium amalgam prepared by electrolysing NaOH solution for 16 hours at 4.5 amps was then introduced slowly over a period of 90 minutes. During this addition the reaction mixture was stirred vigorous and stirring was continued for minutes after amalgam addition had ceased. Amalgam addition was stopped when the precipitated sodium bicarbonate made proper stirring of the liquid diflicult. The temperature of the reactants was kept below 35 C.

The carbon dioxide inlet tube, the stirrer and the amalgam inlet tube were then disconnected from the vessel and 6 N hydrochloric acid was slowly run into the flask until most of the sodium bicarbonate had been decomposed. The carbon dioxide given ofl was led through the traps immersed in Dry Ice/acetone. The mercury layer was run oif, and the remaining contents of the vessel were transferred to a 5 l. round-bottom flask; 500 ml. of water was added and the pH was adjusted to about 7 by the addition of hydrochloric acid and ammonia, The flask was then fitted for distillation with a condenser and a receiver and the unreacted acrylonitrile was distilled oil". When the distillate had distilled over at 100 C. for 5 TABLE I Reactants Reaction products Quarternary Ammonium Salt N,N-di- Relative Percentmethyl age (weight Water p-nitroso- Ex. Mole mole, aniline, Cr+++, Adipo- Propio- Insoluble polymer Other volatile No. Compound percent percent p.p.m. p.p.rn. nitrile nitrile formation impurities formed 3 None-control 8 5 17 83 Not determined Some.

4 None-control but instead tertiary 2.0 8 5 8 do Not determined.

amino-treithanolamine-added.

g "}Cetyltrimethyl-ammonium bromide g g }Small amount {Small amount.

7 Tetraethylammonium p-toluene 0. 18 8 50 73 27 do Do.

sulphonate.

8 do 5. 7 8 50 96 4 do Appreciable quantity of yellow by-produet.

5. 7 8 99 1 None Small amount. 5. 7 16 1 50 99 1 .d0 Very small amount.

10 16 1 50 d do 5. 7 16 1 5 Cetyltrimethylammonium bromide 1. 0 16 1 5 14 Tetramethyl ammonium p-toluene 2. 5 16 1 5 sulphonate. I; do 5 l6 1 1, 000 16.-. Distearyldimethylammonium 1 16 1 chloride. 17 Tetraethylammonium p-toluene 4 66 1 5 sulphonate.

19 Cetyltrimethyl ammonium bromide 2. 4 81 1 5 Not detectable.

EXAMPLE 21 A further experiment was conducted on a larger scale to permit more accurate assessment of the yield and purity of the product.

The reactor consisted of 5 l. three-necked round bottom Pyrex glass flask having an outlet fitted with a tap in the bottom. The flask was provided with a sealed in dip-tube reaching near the bottom of the inside of the flask, so that during operation its outlet was well submerged in the reaction mixture, and connected to a source of carbon dioxide. Through one neck a sealedgland glass stirrer was fitted; to the second neck a 500 ml. separating funnel serving as reservoir for the amalgam was connected and the third neck used as the gas exit line was connected to two liquid traps immersed in Dry Ice/acetone and was then vented to atmosphere. A ring shaped distributor was mounted around the top half of the flask, so that an adjustable flow of cooling water could be passed over the outside of the flask,

The reaction mixture consisting of:

min. the distillation was stopped. The volume of acrylonitrile in the receiver and in the cold traps and the volume of water in the distillation receiver were recorded.

The solution remaining in the flask was transferred to a 1 l. separating funnel and approximately 1 l. of water was added. This solution was extracted five times with ml. lots of methylene chloride. The two phases separated out in approximately 1 hour in the first extraction. However, in later extractions, more and more stable emulsions were formed. It became necessary to centrifuge these emulsions for a considerable time to achieve phase separation. The methylene chloride extract was washed four times with small lots of water, and was then transferred to a weighed flask.

Volatile material were stripped off under reduced pres sure and the remaining non-volatile liquid was weighed. A sample of this liquid was analysed by infra-red spectroscopy and appeared to be pure adiponitrile, but liquid chromatography revealed the presence of oligomeric impurities in this crude material.

Mass balance:

Crude adiponitrile recovered g 109.3

Theoretical yield of adiponitrile on acrylonitrile consumed g 110.5 Yield of crude adiponitrile on acrylonitrile consumed percent 99.0 Acrylonitrile feed reacted (conversion) do 54.3 Purity of crude adiponitrile do 75 Yield of pure adiponitrile on acrylonitrile reacted percent 74 EXAMPLE 22 The apparatus, reaction mixture and method of operation were identical to that used in Example 21.

After the reaction concentrated hydrochloric acid was added while the contents of the flask were still stirred. A slight excess of hydrochloric acid over that required for the neutralisation of the sodium bicarbonate was added. The mercury was run off, and the remaining solution was transferred to a 1 l. flask. Approximately 500 ml. water was added. The flask was fitted for distillation with a condenser and receiver and the unreacted acrylonitrile was distilled off. A trap immersed in Dry Ice/ acetone was fitted to the outlet of the receiver. The distillation was stopped when the distillate had come over for 5 mins. at 100 C. The amounts of acrylonitrile in the receiver, and in the cold traps as well as the amount of water were recorded.

The remaining liquid in the flask was transferred to a separating funnel, and the aqueous and organic phases were separated. The organic phase was washed three times with 25 ml. lots of saturated brine, then dissolved in -1S0 ml. methylene chloride and washed twice with 50 ml. lots of water. The washings were added to the aqueous phase. The methylene chloride extract was transferred to a weighed flask. The volatile materials were stripped off under reduced pressure (70 C. at 20 mm. Hg.) and the remaining non-volatile liquid was weighed.

The aqueous layer was transferred to a 3 l. beaker and the volume was brought up to 1500 ml. with water. The pH was adjusted to approximately 7 using concentrated ammonia. A solution of 100 g. Na Cr O containing a quantity of Celite 535 filter aid (registered trademark) was added slowly while stirring vigorously. The precipitated complex (Cetavlon 3Na Cr O see Ref. I. Renard J. Pharm. Belg. 7, 403-8 (1952)) was filtered off, and washed once with water. The precipitate was dissolved in 300 ml. hot acetone and reprecipitated by adding it slowly while stirring to approximately 2 1. water. This precipitate was filtered oif. Both filtrates were extracted separately with 6 lots of 50 ml. of methylene chloride each, the extracts were combined and transferred to a weighed flask. The volatile materials were stripped oif under reduced pressure (70 C. at 20 mm. Hg), and the remaining nonvolatile liquid was weighed.

Both lots of crude product were combined and a sample was subjected to infra-red analysis by which it appeared to be substantially pure adiponitrile, free from propionitrile, but oligomeric impurities were shown to be present by liquid chromatography.

Mass balance:

Acrylonitrile feed ml 250 Acrylonitrile recovered ml 107.1 Acrylonitrile consumed ml 142.9 Theoretical yield of adiponitrile on acrylonitrile consumed percent 99.1 Total crude adiponitrile recovered g 115.4 .'.Yield of crude adiponitrile on acrylonitrile consumed percent 99.1 Acrylonitrile feed reacted do 57.2 Purity of crude adiponitrile do 75 Yield of pure adiponitrile on acrylonitrile reacted do 74 12 EXAMPLE 23 This experiment demonstrates the reaction without deliberate addition of promoters, and using reagents from which the usual impurities were removed by careful purification, i.e. reagents which contained considerably lesser amounts of promoters than might be encountered in commercial reactants. The quaternary ammonium compound was purified by two recrystallisations; once-distilled water water and acrylonitrile were purified by distillation. Mercury of Analar purity was purified further by passing it three times in fine droplets through a 3 ft. high column of 20 nitric acid (analytical grade).

The reaction mixture was made up from the purified reagents as:

Cetyltrimethylammonium bromide g 10 H O ml 30 Acrylonitrile ml 30 N,N-dimethylparanitrosoaniline mg 0.06 Mercury ml 50 All vessels for the preparation of the reagents and for the reaction were washed with 20% hydrofluoric acid solution and thoroughly rinsed with doubly distilled water. The amalgam was prepared by electrolysing 50% w./v. aqueous sodium hydroxide solution (made up from Analar sodium hydroxide) in a mercury pool, used as cathode.

The reaction vessel consisted of a 250 ml. three-necked flask having an outlet in the bottom. A dip-tube was provided as carbon dioxide gas inlet. The carbon dioxide gas outlet connected to two traps immersed in a carbon dioxide/acetone bath and a glass stirrer were also fitted, all as described in Example 22.

The vessel was flushed out with carbon dioxide. Stirring of the aqueous/ organic phase was commenced and amalgam was slowly added to the vessel from a dropping funnel. The flask was placed in a water bath for cooling. The temperature of the reaction was kept below 35 C. Amalgam addition was stopped when the amount of precipitated sodium bicarbonate made the etficient stirring of the solution difficult. The carbon dioxide inlet was removed and concentrated hydrochloric acid was slowly added to the solution from a dropping funnel until the sodium bicarbonate had been destroyed. The spent amalgam was run off, and the remaining contents of the vessel were transferred to a flask. This was connected for distillation and the unreacted acrylonitrile was distilled over.

The liquid remaining in the flask was transferred to a separating funnel and the organic layer was separated off. This was washed four times with a saturated sodium chloride solution and the washings were added to the aqueous layer. The volatile materials were stripped from the washed organic layer under reduced pressure, and the remaining non-volatile matter was weighed.

The pH of the aqueous layer was adjusted to 7 with ammonia, and distilled water was added to bring the volume to about 400 ml. A solution of 10 g. Na Cr O in 50 ml. of water containing Celite filter aid was added slowly with stirring. The precipitate formed was filtered off and washed several times with water. It was then dissolved in approximately 40 ml. of acetone and reprecipitated by the addition of 500 ml. of water. The precipitate was filtered olf and washed a number of times. The filtrates and washings were combined and extracted six times with 50 ml. lots of methylene chloride.

The volatile materials were stripped from the extract and the remaining non-volatile liquid was weighed.

Both lots of product were subjected to analyses scribed in Example 21.

as de- Mass balance:

Acrylonitrile fed ml 30.0 Acrylonitrile recovered ml 9.9 Acrylonitrile consumed "ml-.. 20.1

following mixture of reagents was introduced into the Theoretical yield of adiponitrile on acryloniflask:

trile consumed g 16.4 Actual yield of crude adiponitrile g 16.25 A ry 2 Yield of crude adiponitrile on acrylonitrile 5 Trlmcthylcetylammonrum brornlde g 0.6 consumed percent 99.1 H O I ml 0.5 Acrylonitrile feed reacted do 67 NaH PO -2H O g 0.19 Purity of crude adiponitrile do 75 Na i-IP g 0.17 Yield of pure adiponitrile 0n acrylonitrile re- CrC1 61-1 0 mg acted do 74 10 N,N-dlmethyl-p-nitrosoanllme "micrograms-.. 2 H ml 5 EXAMPLE 24 g This example demonstrates the use of an inorganic To the reaction mixture 8 of amalgam. p ep as id i h presence f b fie l i set out in Example 1, was added slowly, and s1multane The experiment was carried out as described in Excury with an excess of magnensium filings in a separatlng ample 1, using however a 50 ml. Erlenmayer flask with at such a rate that the solution was maintained between a sealed-in tube for the addition of phosphoric acid. The a pH of 7.0 to 8.0.

TABLE II Reactants Reaction Products Relative N,N-di- Percentage Salt Capable of Forming Alkylated Cations methyl (weight percent) Water p-nitroso- Insoluble Other volatile Mole mole, aniline, 01 Adipo- Propid polymer impurities Ex. No. Compound percent percent p.p.m. p.p.m. nitrile nitrile formation formed 26 Trimethyl(ethyl) ammonium bromide 10 1 5 99 Trimethyl(n-propyl)ammonium bromide 5 1 4 99 Slight Trimethyl(n-butyl)ammonium bromide. 10 1 5 99 Do. Trimethylfisoamybammonium bromide 5 1 5 99 Very slight. Trimethyl(n-amy1)ammonium bromide 5 40 1 5 99 Slight. Trimethyl(ndecyl)ammonium bromide 4.1 40 1 5 99 Do. Trimethyl(cyclopentyl)ammonium 3.6 25 1 5 99 Do.

bromide. Triinethykcyclohexy )ammonium bromide 4. 7 32 1 5 99 Trir'gedthylu-phenyl 2-propyl) ammonium 3. 7 47 1 5 99 10 1 e. Acetylcholine bromide 5. 0 32 1 5 99 Choline chloride h 5.0 32 1 5 42 N ,I g, l( iI,N-tetramethyl ptperazmium 4. 3 32 1 5 89 1O 1 B. N,N-dimethylmorpho inium iodide 3. 0 56 1 5 79 21 Very slight. N,N-,N,N,N,N'-hexamethylethylenediammonium dibromide.

3. 5 49 1 5 98 2 [(CHa)aN.CH2CH2N(CHa)s].2Br-. 40 N,N-dimethyltriethylenediammonium diiodide.

CHzCHa CHaNCH CH2N CHa .21 4.5 32 1 5 97 3 Slight.

CHzC r 41 N,N,N,N,N, -hexamethyl-1,3-propylene- 2.3 40 1 5 47 53 Slight.

diammonium diiodide. Tetramethylphosphonium iodide 2. 4 33 1 5 90 10 Very slight. Trimethyl(p-tolyl) ammonium iodide. 3. 9 39 1 5 Very poor yield Trimethyl(benzyl)ammonium iodide 4.7 33 1 5 High ratio of adiponitr e. propionitrile, but large amount of impurities Girard's Reagent T-trimethyl(hydrazidomethyDammonium chloride.

(CH3)3NC1".CH?.CO.NHNH2. 4. 3 33 1 5 25 75 Very Slight. Dimethyl(diethyl)arn.moniumiodide 8.8 23 1 5 99 1 Slight. Dimethyl(di-n-propyl)ammonium 1odide 4. 6 33 1 5 91. 5 8. 5 Large Dimethyl(di-n-butyl)ammouium iodide 5.0 24 1 5 40 60 Slight. Dimethyl(di-n-decyl)ammonium iodide 2. 9 56 1 5 89 11 Do. Methyl(triethyl)ammonium iodide 6. 6 20 1 5 99 1 Do. Mgthylggiethyl) (n-propyl)ammonium 4. 8 25 1 5 99 1 ronn e. Methyl(tri-n-propyl)ammonium iodide 5.0 32 1 5 87 13 Slight lvIetgyiKn-propyl) (di-n-butyl) ammonium 4. 4 33 1 5 66 34 Do.

10 1 B. MethyKtri-n-butyl)ammonium iodide 5. 2 24 1 5 38 62 Medium-..-- Medium quality. N-methyl-N-ethyl-piperidinium iodide 4.4 33 1 5 99 N-methylpyridinium iodide 4. 8 33 1 5 Extremely small yield of adiponitrile, no propicr nitrile. Blue colour formed. On exposure to air blue colour fades back to original light yellow. 57 N-methylquinohnium iodide 3. 6 39 1 5 Very small yield. Colour changes to dark brown. 53 N-methylisoquinolinium iodide 3. 7 30 1 5 Extremely small yield of adipbonitrile, no propionitrile. Colour changes to dark rown. 59 N,N-dimethy -2-methyl-pyrazinium iodide 4. 1 39 1 5 Very poor yield. Colour changes to dark brown. 60 N,N-dimethyl-3,3-dipyridyhu m iodide 1. 6 76 1 5 Extremely small yield of adiponitrile, no propio- (Paraquat, Registered trademark). nitrile. Blue colour formed. On exposure to air, blue colour fades back to light yellow. Stearyl pyridirium bromide (Fixanol C, 4. 3 10 1 5 Large amount of propionitrile. Colour formation Registered trademark). as for Ex. 60. Triethyl(n-propyl)ammon1um brom1de 4. 4 33 1 5 99 1 Slight Slight. Triethyl(n-butyl)ammonium bromide. 4. 0 39 1 5 99 Do. Triethyl(n-decyl)ammonium bromide" 4. 1 39 1 5 96 Diethyl(di-isobutyl) ammonium iodide 4. 2 33 1 5 99 Ethyl(tri-n-propyl)ammonlum bromide- 3.9 39 1 5 97.5 Do. Ethyl(tri-n-butyl)ammonium iodide" 6. 4 33 1 5 43 Do. Tetra(n-propyl) ammonium iodide 5. 0 33 1 5 Do.

The reaction mixture was worked up as described in Example 1 and the adiponitrile was analysed by gas liquid chromatography. No propionitrile was detected; the yield of the crude product on acrylonitrile was better than 99%, purity of the crude adiponitrile was better than 70%, i.e. the yield of pure adiponitrile was about 70%.

EXAMPLE 25 A magnesium amalgam was prepared by shaking mercury with an excess of magnesium filings in a separating funnel and running out the amalgam so formed. The amalgam was prepared and handled under an atmosphere of nitrogen. This amalgam was then substituted for the sodium amalgam in a hydrodimerisation reaction of acry-' lonitrile as described in experiments 3 to 20 inclusive. The quaternary ammonium salt was cetyltrimethylammonium bromide (1 mole percent), water content was 16 mole percent, N,N-dimethylparanitrosoaniline was 1 p.p.m., Cr+++ content was 5 p.p.m. and the crude reaction product, on infra-red analysis appeared to consist of more than 99% adiponitrile; however, oligomeric impurities were shown to be present by liquid chromatography. No propionitrile was detected in the crude prodnot. The yield of crude product on acrylonitrile consumed was better than 99%, purity of the crude product was better than 70%. Thus the yield of pure adiponitrile reacted thus was about 7 However, reaction rate was slower than with sodium amalgam.

EXAMPLES 2668 A further series of small scale experiments as described for Examples 3 to 20 was carried out to determine the etfectiveness of other compounds capable of forming alkylated cations. Results are given in Table II and are expressed in the same manner as described for Examples 3 to 20.

EXAMPLE 69 Experiments 69 to 70 were carried out to determine the elfect of elevated temperature on the proportion of propionitrile formed.

The experimental arrangement was as described for Example 23 using, however, commercial grade, unpurified chemicals. The reaction mixture consisted of:

Cetyltrimethylammonium bromide g 12 Acrylonitrile ml 15 Water ml 30 CrCl -6H O mg 0.6 N,N-dimethylparanitrosoaniline micrograms 60 Mercury ml 20 COMPOSITION OF REACTION MIXTURE (h/w.)

Acrylonitrile Adiponitrile Propionitrile This example demonstrates the slight increase in the amount of undesired propionitrile formed at elevated temperatures; it also shows that at the initial lower conversions the proportion of propionitrile was substantially lower.

16 EXAMPLE 70 The previous example was repeated, keeping the temperature at 501-2 C. throughout the reaction. The following results were obtained:

COMPOSITION OF REACTION MIXTURE This example demonstrates the further increase in propionitrile with higher temperatures and again the lower propionitrile proportion at lower conversions.

EXAMPLE 71 The reactor described in Example 1 was charged with 20 mls. of mercury, flushed with carbon dioxide and then 0 a mixture was added consisting of g. of ethyl acrylate,

6.86 g. of tetraethylammonium p-toluene sulphonate dissolved in g. of water, 20 g. of dimethylformamide and 20 microgrammes of N,Ndimethyl p'nitrosoaniline. 60 mls. of sodium amalgam prepared as in Example 1 was then added to the reactor over a period of 60 minutes; during this time the flask was agitated vigorously and the temperature was maintained between 25 and 40 C. The aqueous phase was then extracted 10 times with 10 mls. each of methylene chloride, the combined extracts were washed twice with 20 mls. of water and the methylene chloride and other volatiles were evaporated off on a water bath. The residue after evaporation was dried for 10 minutes at 130 C. to remove the water. Infrared spectroscopic analysis of the crude product obtained showed the spectrum of diethyladipate.

EXAMPLE 72 Example 71 was repeated using, however, 6.6 g. of

crotonitrile instead of 10 g. of ethyl acrylate and a lesser 4 amount of dimethylformamide, namely 10 g. only. Reaction conditions and work-up for analysis were as described in Example 71. By vapour phase chromatography the crude reaction product was shown to contain 3,4-dimethyl adiponitrile together with unreacted crotonitrile.

EXAMPLES 73-81 INCLUSIVE Examples 73 to 81 demonstrate the effect of conducting the reaction at a pH between 1.5 and 9.5 in the presence and absence of quaternary ammonium salts. Experiments 73 to 81 were carried out as follows.

The reaction was conducted in a closed jacketed 3-necked glass vessel of 350 ml. capacity, fitted with a glass stirrer. Amalgam as prepared in Example 1 flowed through the vessel at a controlled rate by means of inlet and outlet tubes in the base of the reactor, the depth of mercury being maintained at a level of 0.5 cm. Temperature was 32:3 C.

In Experiments 73 to 75 inclusive the pH of the solution was controlled at 1.5-2.5 by the dropwise addition 60 from above, simultaneous with the addition of amalgam, of 11 N hydrochloric acid in the presence of thymol blue as indicator. In Examples 76 to 78 inclusive the reaction was carried out at a pH of 4-5 by employing a 0.1 molar phosphate buffer and neutralising during the reaction by addition of concentrated hydrochloric acid in the presence of 'bromocresol green as indicator. In Examples 79 to 81 inclusive the reaction was conducted at a pH of 8.21-05 in the presence of a bicarbonate buffer, as described in Example 1. A dip tube for introduction of carbon dioxide was included in the apparatus.

Examples 73, 76 and 79 demonstrate the reaction in the absence of a quaternary salt; Examples 74, 77 and 80 demonstrate the reaction in the presence of 30 g. of triethylmethylammonium p-toluene sulphonate and Examp es 75 78 and 81 demonstrate the reaction in the pres- 17 once of 30 g. of trimethylcetylammonium bromide. To 100 ml. of water containing the above stated pH controlling agents and, where used, the quaternary ammonium salts, the following further reagents were added: 13.2 g. of acrylonitrile, 0.012 mg. of N,N-dimethyl p-nitrO- N, P or S atom of the said ammonium, phosphonium or sulphonium salt, respectively, the other valences of said atom being satisfied by linkages to saturated carbon atoms joined directly to said N, P or S atom, said cation being free from substituents which interfere with the reductive soaniline and 10 ml. of mercury. After the reaction had dimerization, and maintaining said liquid medium at a pH been completed, the reaction mixture was removed from of at least 1.5 and at a temperature less than 60 C.

the vessel and a sample was withdrawn from gas chro- 2. A process according to claim 1 wherein the pH of matographic analysis for residual acrylonitrile, propiothe liquid medium is maintained in the range between 7.0 nitrile and adiponitrile. In the case of Examples 75, 78 and 9.5 and the amount of onium salt is between 0.5 to and 81, the high boiling nitriles were then removed and 50 parts per 100 parts starting materlal.

extracted from the remainder of the solutions as described 3. A process as claimed in claim 1 wherem the liquid in Example 23; in the case of Examples 73, 74, 76, 77, medium is maintained at a temperature within the range 79 and 80 the higher boiling nitriles were extracted from of from 35 C. to 60 C.

the remainder of the solution as described in Example 1. 4. A process as claimed in claim 1 wherein said onium A portion of each extract was then subjected to ga cations are tetraalkyl ammonium cations. chromatographic analysis to determine the percentage of 5. A process according to claim 1 wherein a polymerizaadi-ponitrile. tion inhibitor is added.

The impurities in the extract determined by difference 6. Aprocess as claimed in claim 1 wherein acrylonitrile were considered to be higher hydrooligomers of acrylois reductively dimerized to form adiponitrile, the amalgam nitrile other than adiponitrile. is alkali metal amalgam, the liquid medium comprises Results are giveninTable III. water and the cations are tetraalkyl ammonium cations.

TABLE III Reaction Products (weight percent) Percent Higher conversion Adipo- Propiohydroof acrylo- Example No. Quaternary ammonium salt pH nitrile nitrile oligomers nitrile feed 73 None 14.7 79.8 5.5 70 74..-. riethylmethyl-ammonium p-toluene sulphonate }1.5 to 2.5---- 46. 3 48. 7 5.0 69 75.... Trimethyl-cetyl ammonium bromide 77. 2 11. 4 11. 4 96 76..-- one 14. 0 s1. 1 4. 9 s1 77 Triethylmethyl-ammonium p-toluene sulphonate }4 to 5 36. 5 54. 5 9. 0 68 78. Trimethyl-cetyl-ammonium bromide 67. 3 15. 4 17. 3 92 79.- None 7. 7 86. 9 5. 4 53 80.- Triethylmethyl-ammonium p-toluene su1phonate }8.2=l:0.5--. 61. 4 32. 8 5. 8 78 Trimethyl-cetylammonium bromide 75. 7 5. 4 18. 9 86 EXAMPLES 82-87 INCLUSIVE Examples 82 to 87 inclusive demonstrate the effect of increasing the water-acrylonitrile ratio on the proportion of higher hydro-oligomers in the crude product.

In Experiments 82, 83 and 84 apparatus, conduct of the experiment, work-up and analysis were as described in Example 81 using, however, 100 g. of water, g. of cetyltrimethylammonium bromide, 0.015 mg. of N,N-dimethyl p-nitrosoaniline and acrylonitrile in the molar proportions indicated in Table IV. Experiments 85, 86 and 87 were conducted essentially in a similar manner on semi-technical scale in a continuous (steady state) glass reactor where the collected reaction mixture after completion of the run was about 5 1. volume. Results, indicating the reduced proportion of higher hydro-oligomers at higher water/acrylonitrile ratios, are g1ven 1n Table IV.

TABLE IV Reaction Product Percent Molar by weight Percent ratio, conversion water: Higher of acrylo- Adipo- Propiohydroacrylo- Example No. nitrile nitrile nitrile oligomers nitrile We claim:

1. In a process for the reductive dimerization of acrylonitrile, a lower alkyl-substituted acrylonitrile or a lower alkyl acrylate to obtain the corresponding adiponitrile, lower alkyl-substituted adiponitrile or lower alkyl adipate, respectively, wherein a liquid reductive dimerization medium containing the said nitrile or said acrylate is brought into contact with an alkali metal or alkaline earth metal amalgam, the improvement which comprises including in said liquid medium, a water-soluble ionizable alkylated quaternary ammonium or phosphonium or tertiary sulphonium salt whose anion is non-reactive and whose cation includes at least one alkyl group attached directly to the 7. A process as claimed in claim 6 wherein the pH of the liquid medium is maintained in the range of from 7.5 to 9.5 by supplying carbon dioxide thereto.

8. A process as claimed in claim 6 wherein said liquid medium contains in solution therein from 0.1 to 10 mole percent of a quaternary ammonium salt as the source of said alkylated onium cations, and the molar ratio of acrylonitrile to water in said liquid medium is within the range of from 10:1 to 1:70.

9. A process according to claim 6 wherein the liquid medium contains a polar organic solvent together with water.

10. A process as claimed in claim 6 wherein the liquid medium further contains dimethyl formamide.

11. A process as claimed in claim 1 wherein the salt is a quaternary ammonium salt which is soluble in said medium, said salt having the formula:

R R R R NX wherein X is an anion, R and R separately, are selected from the group consisting of methyl, ethyl, propyl, isopropyl and isobutyl, R is selected from the group consisting of alkyl of from 1 to 24 carbon atoms, cyclopentyl and cyclohexyl, and R separately represents alkyl of from 1 to 24 carbon atoms, or R and R together form with the quaternary nitrogen atom a saturated heterocyelic ring optionally containing in the ring, in addition to the said nitrogen atom and carbon atoms, a single nitrogen, oxygen or sulphur atom.

12. A process according to claim 11 wherein R R and R are selected from the group consisting of methyl and ethyl.

13. A process according to claim 11 wherein any one of R R R and R bears a substituent other than an aromatic ring in the u,;8 position to the quaternary nitrogen.

14. A process according to claim 2. wherein the pH is controlled by neutralization of the amalgam with a weak acid having a dissociation constant smaller than 1x 10-*, the resulting salt operating as a buffer.

15. A process according to claim 2 wherein the pH is controlled by means of an alkali metal phosphate buffer.

16. A process for the hydrodimerization of acrylonitrile to form adiponitrile which comprises intimately contacting a preformed sodium amalgam with an aqueous solution of acrylonitrile having dissolved therein an alkylated quaternary ammonium salt, the cation of which is selected from the group consisting of tetramethyl ammonium, tetraethyl ammonium, methyl triethyl ammonium and cetyl trimcthyl ammonium and the anion of which is selected from the group consisting of toluene sulphonate, bromide and chloride, at a temperature of 10 to 60 C., maintaining the pH of said solution between 7.0 and 9.5 during said contact and recovering the resulting adiponitrile, said solution containing from 0.5 to 50 parts by weight of said quaternary ammonium salt per 100 parts of acrylonitrile and the molar ratio of acrylonitrile to water therein being in the range of 10:1 to 1:20.

References Cited UNITED STATES PATENTS 3,140,276 7/1964 Forster 20472 XR 3,193,477 7/1965 Baizer 20472 XR 5 3,193,480 7/1965 Baizer et a1. 20472 XR 3,245,889 4/1966 Baizer et al 20472 XR 3,250,690 5/1966 Baizer et a1.

3,225,083 12/1965 McClure 260465.8

FOREIGN PATENTS 1,366,081 6/ 1964 France.

1,472,033 1/ 1967 France.

US. Cl. X.R. 

